fix: don't group floating windows unless one is fully contained in the other

[sid-6581]

What kind of change does this PR introduce?

• Fix

Did this PR introduce a breaking change?

• No

This is an attempt to make it less likely that floating windows with consecutive z-indexes are rendered together if they shouldn't be rendered together, like the first screenshot in #2502.

Instead of checking if the window rects intersect, I check if one is contained in the other. This isn't foolproof, because we could still have windows with consecutive indexes that should not be rendered together (like the first screenshot in #2502, but in a bigger directory), so the whole window grouping thing needs a lot more thought, and should probably be able to be disabled entirely by an option.

Still, I can't think of any time it would make sense to render two windows with consecutive z-indexes together if one isn't fully contained in the other.

[github-actions]

Test Results

  6 files  ±0    6 suites  ±0   14s ⏱️ -4s
110 tests ±0  110 ✅ ±0  0 💤 ±0  0 ❌ ±0 
644 runs  ±0  644 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit a7e24de. ± Comparison against base commit 5efb713.

[fredizzimo]

I think this looks good, but it's better that @Kethku double checks, since she knows the details better.

[fredizzimo]

Thanks, I decided to merge this, since it's strictly better than the previous behaviour, although not perfect.